1. Field of the Invention
The present invention is a COMA (code division multiple access) receiving apparatus, and more particularly, to a COMA receiving apparatus which carries out a transmission power control.
2. Description of the Related Art
In a CDMA communication system, a transmission power control is carried out to keep reception quality on the receiving end. In the transmission power control used for the COMA communication system, a transmission power control bit (TPC bit) is generally used.
FIG. 1 shows a section for generating the TPC bit in a conventional CDMA receiving apparatus. The CDMA receiving apparatus is composed of a receiving antenna 101, a quasi-synchronization detecting circuit 102, an A/D (analog-to-digital) converter 103. a synchronization tracking circuit 104, a despreading circuit 105, a demodulating circuit 106, an SIR (signal-to-interference plus noise power ratio) estimating circuit 107, a TPC bit generating circuit 108. The receiving antenna 101 outputs a reception signal to the quasi-synchronization detecting circuit 102. The quasi-synchronization detecting circuit 102 converts a reception signal into a signal having a frequency band for a baseband process, i.e., a baseband signal, and outputs to the A/D converter 103. The A/D converter 103 A/D-converts the reception signal and outputs to the synchronization tracking circuit 104 and the despreading circuit 105.
The synchronization tracking circuit 104 carries out path searches using a spreading code for a specific user and outputs a path delay quantity of the path with the highest correlation with the spreading code among the searched paths to the despreading circuit 105. The despreading circuit 105 despreads the baseband signal based on the path delay quantity and outputs to the demodulating circuit 106. The demodulating circuit 106 carries out a bit phase adjustment to the reception signal and outputs to the SIR estimating circuit 107. The SIR estimating circuit 107 estimates an SIR value based on the demodulated reception signal and outputs the SIR value to the TPC bit generating circuit 108.
The TPC bit generating circuit 108 compares the SIR value and a reference SIR value supplied from a host apparatus (not illustrated) and generates a TPC bit signal based on the comparison result. That is, the TPC bit generating circuit 108 generates the TPC bit signal to increase transmission power, if (reference SIR value)>(estimated SIR value), and generates the TPC bit to decrease the transmission power, if (reference SIR value)<(estimated SIR value).
Such a CDMA receiving apparatus may be provided in a base station and a mobile station. In the transmission power control using the CDMA receiving apparatus, when the base station and the mobile station in a cell of the base station communicate with each other, the mobile station measures the SIR value of the signal transmitted from the base station, and determines the TPC bit signal for controlling the transmission power of the base station based on the measurement result. Then, the TPC bit signal is inserted in a transmission signal and transmitted to the base station. The base station receives the transmission signal from the mobile station, extracts the TPC bit signal from the transmission signal and updates the transmission power in accordance with the TPC bit signal.
The base station measures the SIR value of the transmission signal from the mobile station, and determines the TPC bit signal for controlling the transmission power of the mobile station based on the measurement result. Then, a TPC bit signal is inserted in a transmission signal and transmitted to the mobile station. The mobile station receives the transmission signal from the base station, extracts the TPC bit signal from the transmission signal and updates the transmission power in accordance with the TPC bit signal.
A pilot bit pattern of a known bit pattern is arranged in a transmission signal for every slot (periodically) and the TPC bit signal is arranged for every slot. Therefore, the pilot bit pattern is used as a reference phase signal to carry out quasi-synchronization detection to the transmission signal and to measure an SIR value.
The CDMA receiving apparatus extracts a pilot bit pattern from the reception slot received from the counter station, measures an SIR value from the pilot bit pattern, and generates a TPC bit signal based on the SIR value. Then, the TPC bit signal is inserted in the transmission slot and transmitted to the counter station. The reception slot used to measure the SIR value and the transmission slot used to insert the TPC bit signal generated based on the SIR value have a one-to-one correspondence relation.
In such a CDMA receiving apparatus, when the path delay quantity is large, the timing of reception of the pilot bit pattern is delayed. As a result, the timings of the generations of the SIR value and the TPC bit signal are delayed. Therefore, it sometimes becomes not possible to correctly insert the TPC bit signal in the transmission slot.
In conjunction with the above description, a transmission power control apparatus is disclosed in Japanese Laid Open Patent application (JP-A-Heisei 9-284205). In this reference, a reception SIR measuring apparatus uses a signal in which a known pilot signal is inserted in a data signal with a predetermined interval. A detecting section carries out interpolation synchronization detection using the pilot signal. A power value of data symbol determined through the interpolation is calculated. A summation of the power values of the data symbol is calculated over predetermined pilot signal intervals. A difference in the power value from a fading envelope at the same sampling time as the data symbol determined is calculated. The power value differences are summed over predetermined pilot signal intervals. Then, a ratio between the summation of power values of the data symbol and the summation of the power value differences is calculated, and the ratio is used as an SIR.
Also, a method of controlling transmission power in a CDMA mobile communication system Is disclosed in Japanese Laid Open Patent application (JP-A-Heisei 10-145293). In this reference, a first communication apparatus detects a signal level of a communication signal from a second communication apparatus at a predetermined timing. A transmission power control signal is generated based on the detected signal level and arranged in a transmission signal from the first communication apparatus to the second communication apparatus at a predetermined position.
Also, a method of measuring a reception SIR is disclosed in Japanese Laid Open Patent application (JP-A-Heisei 10-13364). In the reference, a synchronization detecting apparatus on a receiving side carries out synchronization detection to a signal in which a known pilot signal is inserted in an information signal in a predetermined in the transmission side. The synchronization detecting apparatus calculates a power value of a fading envelope obtained by interpolation on a complex signal space of a baseband. The power value is averaged in the predetermined pilot signal interval, and the average value is handled as a reception desired wave power. A ratio of the received data symbol and the fading envelope obtained by the interpolation is calculated on the complex signal space, and the ratio is multiplied by the square of the fading envelope. A signal point is determined based on the multiplying result and the fading envelope containing an interference ingredient is calculated using the received data symbol and the determining value. A difference between the calculated value and the interpolated fading envelope is calculated. The square of the differences is integrated over the pilot signal interval. The integrated values are averaged over a plurality of pilot intervals. The average value is handled as a reception interference wave power. Then, a ratio between the reception desired wave power and the reception interference wave power is set as a SIR value.
Also, a radio communication apparatus is disclosed in Japanese Laid Open Patent application (JP-A-Heisei 11-331071). In this reference, a data arrangement determining section determines the arrangement of pilot data and transmission power control data containing the transmission power control information which is based on the measurement result of a reception quality in the slot based on a processing delay and a propagation delay which are needed to control transmission power. A slot offset setting section sets an offset for the slot position relation between an upward channel and a downward channel.
Also, a mobile communications system is disclosed in Japanese Patent No. 2,785,804. In this reference, a carrier signal is expressed by an in-phase component and an orthogonal component and a carrier signal detecting section detects a carrier signal point for every constant period. An amplitude correcting section corrects the amplitude of the carrier signal point based on previous transmission power control values. An estimating section estimates the carrier signal point where the transmission power control is next carried out, using the carrier signal point with the amplitude corrected. A comparing section compares power at the estimated carrier signal point with a predetermined reference value. A transmission power control unit generates a transmission power control value when the transmission power control is next carried out based on the comparison result. A memory stores and supplies the transmission power control value to the amplitude correcting section as the previous transmission power control value. A transmitting section transmits the transmission power control value. A base station includes the above sections and a transmission power control circuit. Each of a plurality of mobile stations is connected with the base station using an identical frequency electric wave, and is controlled based on the transmission power control value transmitted from the base station such that the reception signal powers from the plurality of mobile stations in the base station are equal to each other.